Callanish Stone Circle is estimated to have been constructed about 2900 - 2600 BC possibly before 3000 BC making the structure older than the Great Pyramid of Giza. The 13 primary stones form a circle about 13 m in diameter, with a long approach avenue of stones to the north, and shorter stone rows to the east, south, and west. The overall layout of the monument recalls a distorted Celtic cross. The individual stones vary from around 1 m to 5 m in height, with an average of 4 m, and are of the local Lewisian gneiss. It has been speculated, among other theories, that the stones may have formed a calendar system based on the position of the moon. Nobody really knows what this stone circle was made for I guess it's a case for the X-Files.